Recently a liquid crystal display panel, a kind of flat display, has been widely used as a display of a lap-top word processor and an electronic pocketbook.
As shown n FIGS. 16(a) and 16(b), in a liquid crystal module adopting the above liquid crystal display panel, TCPs 63 with drive IC chips 62 thereon are used in connecting a liquid crystal display panel 61 and the IC chips 62 for driving the liquid crystal display panel 61. Each of the TCPs 63 is connected to a PWB (Printed Wiring Board) 64. The liquid crystal display panel 61, the TCP 63 and the PWB 64 are, as shown in FIG. 17, connected so as to virtually form one flat plane. FIG. 17 is an enlarged cross-sectional view of the area enclosed with a circle in FIG. 16(a). Referring to FIGS. 16(a), 16(b), and 17, the member 80 is a bezel case; the member 81 is a plastic chassis; the member 82 is a light guiding plate of a backlight; the member 83 is a spacer; the member 84 is a cold cathode tube for the backlight.
The TCP 63, as shown in FIG. 18(a), has a base film 67 made of flat insulating resin having a device installment aperture 67a in the center thereof. The IC chip 62 is fixed to the device installment aperture 67a by resin mold 68. Input wiring patterns 65 and output wiring patterns 66 are provided on the back surface of the base film 67. An end of each input wiring pattern 65 is connected to each terminal of the IC chip 62, while the other end of each input wiring pattern 65, extending to the left in FIG. 18(a), has an input terminal 65a. An end of each output wiring pattern 66 is connected to each terminal of the IC chip 62, while the other end of each output wiring pattern 66, extending to the right in FIG. 18(a), has an output terminal 66a.
FIG. 18(b) is a cross-sectional view showing the liquid crystal display panel 61 and the PWB 64 connected to each other. Each of the input terminals 65a of the TCP 63 is connected through an ACF (Anisotropic Conductive Film) 69 to each of output terminals 70a provided on an end of each of electrode patterns 70. Each of the output terminals 66a of the TCP 63 is connected through the ACF 69 to each of input terminals 71a provided on an end of each of electrode patterns 71. Solder resist 72 is applied to parts of the input and output wiring patterns 65 and 66 where insulation is necessary.
In a liquid crystal module utilizing such a liquid crystal display panel as the liquid crystal display panel 61, ratio of available display area to the whole front surface should be great in order to improve portability and make dimensions scaled down. Referring to FIG. 16(b), the ratio of the area enclosed with alternate long and short dash lines A should be great.
One of the improvements achieved so far to increase the area ratio is to use slim drive electronic parts around the liquid crystal display panel in order to reduce space necessary to accommodate the drive electronic parts (a first conventional method). For example, size of a TCP have been reduced by shortening distances between its input terminals and output terminals. Size of a PWB have been reduced by reducing its width.
Another method is to carve a part of a TCP. The carved TCP is more flexible and therefore can be bent so that the drive electronic parts including a PWB can be provided on the back surface of the panel (a second conventional method).
Recently, as improvements on definition and pixels are achieved with a liquid crystal display panel, especially with a color liquid crystal display panel. Therefore, there is demand for a TCP of high definition and multi-output in accordance with the improvements on definition and pixels.
However, when a conventional TCP of high definition and multi-output is made slim according to the first conventional method in order to increase the area ratio of the available display area, the following problems occurs.
As shown in FIG. 19(a), when an ACF is used to connect an input terminal of a slim TCP 73 and an output terminal of the PWB 64 in a heating-and-pressurization connecting process, an area which is on the input-terminal side of the TCP 73 and in the neighborhood of the resin mold 68 fixing the IC chip 62 is heated and pressurized. Accordingly, the base film 67 is pulled towards the input terminal which causes a stress within the TCP 73. The base film 67 therefore induces the resin mold 68 to peel at an interface thereof and also induces a copper-foil inner lead to be cut off. The inner lead refers to an inner lead connected to the terminal of the IC chip 62 sticking out in the device installment aperture.
Moreover, in the connecting process, the PWB 64, being still hot and expanded, is attached to the TCP 73 which has been already connected and fixed to the liquid crystal display panel 61. Therefore, when the heating connection process is over and the PWB 64 is cooled down to a room temperature, the PWB 64 is bent in accordance with contraction of the PWB 64 as shown in FIG. 19(b). When the ACF is used in the connection, the contraction of the PWB 64 varies depending on the thermal contraction factor of the PWB 64 in a temperature zone between the Tg (the transition point of the ACF to the glass phase) and an ordinary temperature. When solder is used for the connecting, the contraction of the PWB 64 varies depending on the thermal contraction factor of the PWB 64 in a temperature difference between the freezing point of the solder and an ordinary temperature.
The bent PWB 64 distorts a portion of the TCP 73 as indicated as P in FIG. 19(a). The distorted portion P may twist or even cut off the input wiring pattern 65 made of conductor, such as copper foil.
The slim and narrow TCP 73 cannot absorb the stress caused by the bent PWB 64. As a result, the output side of the TCP 73 is pressed against a glass edge of the liquid crystal display panel 61. And an output terminal of the TCP 73 may be cut off by the glass edge.
The TCP of high definition and multi-output is weak in structure because the wiring pitch thereof is narrow and the cross-sectional area of the input and output wiring patterns thereof is small. Therefore, the above problems occur more often with this type of TCP. And the first conventional method which only reduces the size of the TCP cannot make a slimmer and narrower TCP of high definition and multi-output.
Accordingly, the second conventional method, in which the TCP is bent, was employed to increase the ratio of the available display area to the whole front surface of the module. The second conventional method can surely increase the area ratio. However, the second conventional method has a disadvantage in that the bent TCP makes the liquid crystal module thick in size. Since it is important for the liquid crystal module to be thin as well as to achieve a high area ratio of the available display area, it is not preferable to employ the bent TCP.
Consequently, it was impossible to obtain with the conventional methods a thin liquid crystal module of high definition and a great number of pixels and with a high area ratio of available display area. Thus, there is a big demand for improvements on the structure of the TCP which make it possible to obtain a slim TCP of high definition and multi-output.